Celtic manager Ronny Deila insists Virgil van Dijk does not want to leave the Scottish Premiership leaders in January.
Celtic boss Ronny Deila says keeping his best players will take priority over acquisitions in the transfer window.
Kenny Miller has already sealed a return to the club this summer and talk is rife that another fans' favourite, Kris Boyd, could also be on his way back to Govan for the Championship campaign.
Speaking to Sky Sports News, Clark said: "It will be really tough next season with Hibs and Hearts coming down and there are a lot of other full-time clubs in the division which we never really had last year.
"So we've got to make sure we get a good pre-season under our belt and make sure we are ready for it.
"I'm really looking forward to working alongside Kenny Miller who has loads of international caps and played at the highest level so that can only be good for me to play alongside someone of that quality.
"If Kris Boyd was to come in as well that would be great too as it would keep everyone on their toes. It is good to have healthy competition for places.
"A lot of people say Rangers will be favourites but we know how hard it is going to be and we have got to make sure our focus is spot on."